Terminals operating in wireless communication systems are known which employ a plurality of antennas to co-operate in the form of a smart antenna system. In such a terminal, each antenna is connected to a separate associated receiver chain, as well as to a separate associated transmitter chain. An incoming signal can be received in each of the receiver chains via each of the associated antennas. A known data sequence or pattern included in a signal when transmitted by a transmitting terminal may be used in the receiving terminal including the multiple antennas to estimate from the signals received in each of the receiver chains a value of the propagation distance from the transmitting terminal that the signal has travelled. The propagation distance is known in the art as the ‘channel’. The respective values estimated for the channel using the multiple receiver chains are used in a computation by the receiving terminal to estimate a direction between the transmitting terminal and the receiving terminal. The direction estimated by the receiving terminal including the multiple antennas is employed in a transmission mode by that terminal to direct a transmitted signal back to the original transmitting terminal. Signals are constructed in each of the multiple transmitter chains of the terminal which when sent via the associated multiple antennas form a transmitted beam in the required direction.
Terminals employing multiple antennas as described above may for example be used in WLANs (Wireless Local Area Networks), such as WLANs which operate using procedures specified in the 802.11 standard of the IEEE (IEEE, 1997). This standard referred to herein as the ‘802.11 standard’, defines a protocol for communication between components of the WLAN. Many commercially available products operate in accordance with this standard. WLANs such as those operating in accordance with the 802.11 standard can exhibit one of two different basic network architectures, namely ad hoc and infrastructure-based network architectures. Ad hoc architectures include several client nodes using the same frequency for communication without an infrastructure. Infrastructure-based architectures include an infrastructure node, called an access point or ‘AP’, which may for example comprise a connectivity point to a central computer processor. Several client terminals or nodes are operably connected via an AP. The client terminals may for example be connectivity points providing connectivity to computer peripheral devices.
Many terminals operating in wireless communication systems such as WLANs are powered by a battery or other local energy source and it is desirable to introduce measures in such terminals in order to save energy.